1. Field of the Invention
The present invention relates to an image pickup apparatus and a reference position detection method, and more particularly to an image pickup apparatus with an image stabilization function and a reference position detection method executed in the image pickup apparatus.
2. Description of the Related Art
An image pickup apparatus, typically, a digital still camera, held by a user to shoot an image includes an image stabilization function for reducing instabilities of images formed on a photoelectric transducer due to hand shake. The image stabilization function allows the photoelectric transducer to move in parallel with a plane vertical to an optical axis of a lens thereby reducing movement of an image formed on an image plane of the photoelectric transducer. In the initial setting, the photoelectric transducer is usually positioned at a reference position where the center of the photoelectric transducer coincides with the optical axis of the lens, so that the photoelectric transducer is efficiently moved.
A stage apparatus for positioning a photoelectric transducer at a reference position is known. The stage apparatus includes a fixed support substrate, an XY moving member supported on the fixed support substrate to be movable linearly in particular X and Y directions, which are orthogonal to each other and parallel to the fixed support substrate, and an X-direction position detection means for detecting a relative position in the X-direction of the XY moving member with respect to the fixed support substrate. The X-direction position detection means includes an X light source, an X light-receiving member having a light-received position that can be recognized in the X direction, and a calculation means for calculating the relative position in the X direction of the XY moving member with respect to the fixed support substrate, based on the light-received position of the X light-receiving member. The X light source and the X light-receiving member are fixed side-by-side in the X direction on the fixed support substrate. An X reflection member is fixed on the XY moving member to reflect light emitted from the X light source to introduce the reflected light to the X light-receiving element.
The conventional stage apparatus, however, has a problem in that a pair of the light source and the light-receiving element has to be provided each in the X direction and the Y direction. Furthermore, it is difficult to set a threshold value to adapt to changing environments including temperature, etc. depending on the characteristics of the light source and the light-receiving element. Moreover, in the initial setting, the photoelectric transducer has to be moved to the reference position through the steps of moving the photoelectric transducer to a position detected by the pair of the light source and the light-receiving member and of moving it to the reference position. It thus takes much time to move the photoelectric transducer to the reference position.
A measurement apparatus is also known, which includes a measurement unit for measuring, based on image data output from an image sensor in a camera module, the distance between the position of the central light-receiving element of a plurality of light-receiving elements of the image sensor and the position of the center of the optical axis of an optical system in the camera module on the image sensor. The measurement unit executes: a luminance information obtaining process of obtaining, from the image data, first luminance information for each pixel belonging to a first group of pixels arranged along a first direction in an image of the image data and second luminance information for each pixel belonging to a second group of pixels arranged along a second direction orthogonal to the first direction in said image; a center position specifying process of specifying the position of the center of the optical axis on the image sensor based on both luminance information; and a measurement process of measuring the above-noted distance by assuming the position of the central pixel in the image as the position of the central light-receiving element.
However, the image sensor has to be illuminated with predetermined light. Therefore, although the above-noted apparatus can be applied to an adjustment process in the production line, it cannot be applied during the actual use of the digital still camera, because the image sensor cannot be illuminated with predetermined light outside of the production line.